1. Field of the Invention
The present invention relates to an optical tomographic imaging apparatus. More specifically, the present invention relates to an optical tomographic imaging apparatus used for ophthalmic diagnosis.
2. Description of the Related Art
At present, various ophthalmological apparatuses using optical apparatuses are used. For instance, various optical apparatuses for observing eyes, such as an anterior ocular segment photographing device, a fundus camera, and a scanning laser ophthalmoscope (SLO), are used. In particular, an optical tomographic imaging apparatus by an optical coherence tomography (OCT) using interference phenomenon of multi-wavelength light is an apparatus which can obtain a sample tomographic image at high resolution. The ophthalmological apparatus has become indispensable for out-patient department specializing in retinas. Hereinafter, this apparatus will be referred to as an OCT apparatus.
The OCT apparatus can irradiate measuring beam as low coherent light to a sample and, using an interference system, measure backscattering light from the sample at high sensitivity. In addition, the OCT apparatus can scan the measuring beam on the sample and thereby can obtain a tomographic image at high resolution. For this reason that the OCT apparatus can obtain a tomographic image of a retina in the fundus of an eye to be inspected at high resolution, the OCT apparatus is widely used for ophthalmological diagnosis of retinas. Although, a human eye has involuntary motion of the eye ball, called an involuntary eye movement. Therefore, if the time for the ophthalmological diagnosis of a retina using the OCT apparatus is longer, motion artifacts, which is an irregularity of an image, is caused in the obtained tomographic image of the retina due to the influence of the eye movement.
To prevent motion artifacts, various attempts have hitherto been made. For instance, the document of Christoph K. Hitzenberger, “Simultaneous SLO/OCT imaging of the human retina with axial eye motion correction”, Optics Express Vol. 15, No. 25 (2007), discloses a method of using another OCT apparatus in addition to an OCT apparatus for observing fundus. The other OCT apparatus is an apparatus which uses a light source of 1300 nm to obtain a tomographic image of a cornea and monitors the position of the cornea in an optical axis direction (hereinafter, called a vertical direction) of the OCT apparatus for observing fundus. A method has been proposed to control the reference mirror of the OCT for observing fundus for measurement according to the position of the cornea in a vertical direction. The position of the cornea is calculated using the OCT in this manner to reduce motion artifacts to the tomographic image of the retina due to the influence of the eye movement.
As described above, if the measuring time in fundus observation using the OCT apparatus is longer, image irregularity called motion artifacts due to eye movement is caused in the obtained tomographic image of a retina. In the above document, the consideration for reducing motion artifacts is made. However, since the OCT for observing cornea is used together with the OCT for obtaining the tomographic image of the retina, the apparatus becomes larger and the cost of the apparatus is greatly increased.
In view of the above problems, an object of the present invention is to provide an optical tomographic imaging apparatus which enables an apparatus to be simplified and cost thereof to be reduced without reducing accuracy when position information that the moving part of an object is moved in an optical axis direction of measuring beam is detected to reduce the deformation of a tomographic image due to position displacement in the moving part of the object.